1. Technological Field
The present invention relates to an image forming system.
2. Description of the Related Art
In recent years, in the field of the production print (hereinafter, also referred to as “PP”), a technique for increasing the speed and enhancing the efficiency of the printing process has been developed. As one of the techniques for increasing the speed and enhancing the efficiency of the printing process, it is generally known an image forming apparatus of a series tandem system obtained by connecting two image forming apparatus which are operable alone in series. In the present description, among the image forming apparatuses of the series tandem system, an image forming apparatus located at an upstream side in the paper conveyance direction is referred to as an “upstream apparatus,” and an image forming apparatus located at a downstream side is referred to as a “downstream apparatus.”
In the field of the PP, the “image forming system” is configured by connecting a paper feeder which can supply a large amount of papers to the image forming apparatus of the series tandem system and a post-processing device which performs the post-processing on the paper formed with images to correspond to commercial printings to which a large amount of printing processes are required in a short period of time.
In the image forming system, to suppress the paper jam and maintain the productivity, for the upstream apparatus, the downstream apparatus and the post-processing device, it is important to make constant the intervals of the conveyed paper as much as possible, i.e., keep constant the printing cycles of the upstream apparatus and the downstream apparatus. However, between the upstream apparatus and the downstream apparatus, by unpredictable factors such as the friction between the paper and the paper conveying path and the slipping of the paper relative to the conveying roller, a delay may occur to the paper which is conveyed from the upstream apparatus to the downstream apparatus.
Relevantly, for example, Japanese Patent Application Laid-Open No. 2003-167485 discloses a technique of realizing the synchronization of the printing cycles of the surface and the back surface when an image forming unit of the image forming apparatus forms an image on the surface of the paper, the paper is reversed to be supplied to the image forming unit, and the image is formed to the back surface of the paper. In Japanese Patent Application Laid-Open No. 2003-167485, to perform the two-sided printing in a single image forming apparatus, it is possible to easily realize the synchronization of the printing cycles of the surface and the back surface by obtaining information on the paper conveyance of printing the surface when the back surface is printed.
On the other hand, in the image forming system including the upstream apparatus and the downstream apparatus, since a configuration for exchanging the information on the paper conveyance is not provided between the upstream apparatus and the downstream apparatus, the downstream apparatus may not acquire the information on the paper conveyance at the upstream apparatus. Although it is possible to newly add a configuration for exchanging the information on the paper conveyance between the upstream apparatus and the downstream apparatus, it is possible that the significant cost occurs and it is not realistic.
As described above, in the image forming system, it is difficult for the downstream apparatus to acquire the information on the paper conveyance at the upstream apparatus, and thus, it is not easy to realize the synchronization of the printing cycles between the upstream apparatus and the downstream apparatus. Unless the synchronization of the printing cycle is realized between the upstream apparatus and the downstream apparatus, when the delay in the paper occurs, the deviation in the printing cycle of the downstream apparatus occurs. Further, when the delay is also caused at the succeeding paper, the delay time of the paper at the downstream apparatus is increased and defects such as paper jam may be caused.
To handle such a situation, for example, there is a method in which assuming the delay of the paper from the upstream apparatus, the downstream apparatus delays the start of printing to absorb the delay of the paper from the upstream apparatus, and printing cycles of the upstream apparatus and the downstream apparatus are kept constant. However, this causes a problem that the printing cycle of the downstream apparatus is delayed, the producing capability originally equipped with the upstream apparatus and the downstream apparatus may not be sufficiently exerted, and the productivity of the printing process is lowered.